Hi, @jazon_xd
HAVE YOU READ post #12.
Please can you do those tests?
Tom... 
Nope, completely wrong I'm afraid. Time to read up some stepper driver chip datasheets.
Normally stepper drivers initialize with sqrt(0.5) times the nominal current to
each winding (equivalent to starting at 45 electrical degrees in the quadrature
drive) - basically one winding sees A sin(theta), the other A cos(theta), where theta is the electrical angle, A is the current limit.
This means the total power to the windings is constant during the cycle whatever microstepping is used. This makes sense as the max current rating for a stepper is a thermal limit.
Also note that the current supplied to the motor is not the same as the current pulled from the supply as stepper drivers are buck-converters.
I think what's happening here is that the drive is set to drop the current on idle to a low value (very commonly used to save power in stepper systems as the torque requirement at stationary is typically low - however here that's not the case and full current should be held at idle).
If you fail to find solution but still want to keep this driver - apply single step rotations swapping direction at high speed, this will make a noise but driver will run at full current and keep holding the stepper in average position.
Interesting idea, I will try this. Thank you.
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